1. Field of the Invention
The described technology relates generally to a lighting apparatus, and more particularly, to an organic light-emitting diode lighting apparatus using organic light emitting diodes (OLEDs).
2. Description of the Related Art
An OLED includes a hole injection electrode, an organic emission layer and an electron injection electrode. The OLED is configured to emit light when electrons combine with holes within the organic emission layer and drop to a ground state. An organic light-emitting diode lighting apparatus is a lighting apparatus using OLEDs and functions as a surface light source. Thus, the organic light-emitting diode lighting apparatus may be used for various applications by making use of the merits of the surface light source.
At least one of the hole injection electrode and the electron injection electrode of the organic light-emitting diode lighting apparatus includes a transparent conductive material capable of transmitting light. The transparent conductive material has relatively high sheet resistance. Thus, if the electrode is made of the transparent conductive material, luminance becomes non-uniform due to an unnecessary voltage drop.
Furthermore, although the organic light-emitting diode lighting apparatus is a surface light source, the organic emission layer that emits light will emit rays of light in several directions. Accordingly, in the organic emission layer, light emitted in a direction in which the hole injection electrode crosses the electron injection electrode is effectively used, but rays of light emitted in other directions are lost.
In general, an OLED is sensitive to a change in temperature, so the amount of current of the OLED is increased according to a rise in the temperature. Accordingly, if temperature rises during the operation of the organic light-emitting diode lighting apparatus, luminance differs at every portion of the OLED according to the degree of heat generated from the corresponding portion. As described above, a problem arises because the luminance of the organic light-emitting diode lighting apparatus becomes non-uniform according to a change in temperature.